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Ground effector / Underbody spoiler


ben yip
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Recently, there has been questions about the effectiveness of ground effector / underbody spolier.

Anymore discussion of this thing, please discuss here, instead of my member ride thread.

I have dig up this article in english which might be useful. This should clear up many question about this mod

Part 1

http://autospeed.com/cms/title_Modifying-UnderCar-Airflow-Part-1/A_2455/article.html

Part 2

http://autospeed.com/cms/title_Modifying-UnderCar-Airflow-Part-2/A_2456/article.html

It is going too complicated to a level that I am not qualified to read the analysis

Edited by ben yip
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Because aero that creates downforce requires CFD modelling or wind tunnel time, it's best to aim for a flat undertray, from bunper to bumper, so that the air flow doesn't slow down as much. That in itself will reduce the lift created by the natural shape of a car. For ground effects to work the car needs to be lower than legal ground clearance, so not really an avenue worth pursuing anyway. Just make sure the material you select has a lower flash point them what ever you are encasing. Otherwise you can add some cooling vents, but be aware that these opening will ruin the flow a little bit. I would strongly recommend leaving the rear of the engine bay open so that the air that has been through the radiator and the engine bay has somewhere to go. Also worth looking into is blocking off some of the radiator openings. Most cars come over cooled as they need to work in some pretty warm places.

A visit to Bunnings and you can make something similar to that wind deflector thing in your thread for about $30.

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A visit to Bunnings and you can make something similar to that wind deflector thing in your thread for about $30.

Bingo, couldn't agree you more Dave. But apparently, well so I am told, it is more that an angled piece of steel. :whistling:

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That Auto Speed article seems to be more concerned about the effects of drag caused by airflow near the tires/wheels. The 'Ground Effector' kits in question here appear to sit more inwards on the car on the chassis rails. The effects of them can't simply be compared to an article that is looking at something else.

On top of that the ones that you bolt onto your car don't have any flat surface leading up to them if you know what I mean. What's stopping air from just going up and over it instead of just down?

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It would appear then that to have any real benefit on your car, you would need to fabricate a custom solution that best addresses your particular vehicles aerodynamic weaknesses.

I doubt a universal piece of angle (that could be made for about $30) would make a realistic difference then. Further it also appears that randomly placing additional pieces under your car may actual worsen the vehicle's aerodynamics compared to stock standard.

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A full underbody cover is targeting about 15% of the drag, but you will in no way eliminate it. I'd expect you would reduce it to around 10% if done correctly. Once you add mechanical losses, you may have saved 3 - 4% of the total constant speed losses. You will have also added around 1 - 2% of mass, which you have to accelerate and brake all day every day. It also means more difficulty servicing and repairing.

So unless you only drive at 100km/h 95% of the time, I suggest you won't be a winner.

Edited by 450HP/tonne
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